Silicon germanium-on-insulator formation by thermal mixing

ABSTRACT

A layer of amorphous silicon is formed on a germanium-on-insulator substrate, or a layer of germanium is formed on a silicon-on-insulator substrate. An anneal is then performed which causes thermal mixing of silicon and germanium atoms within one of the aforementioned structures and subsequent formation of a silicon germanium-on-insulator material.

RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application Ser. No.61/939,262, filed on Feb. 12, 2014, the entire content of which isincorporated herein by reference.

BACKGROUND

The present application relates to semiconductor manufacturing, and moreparticularly to methods of fabricating a silicon germanium (hereinafter“SiGe”)-on-insulator (hereinafter “SGOI”) material in which thermalmixing of either a layer of silicon formed on a germanium-on-insulator(hereinafter “GeOI”), or a layer of germanium formed on asilicon-on-insulator (hereinafter “SOT”) is employed.

Crystalline Si_(1-x)Ge_(x) is attractive for both bipolar and metaloxide semiconductor field effect transistor (hereinafter “MOSFET”)applications. High performance p-channel MOSFETs consisting of a SiGechannel are in use in 22 nm complementary metal oxide semiconductor(hereinafter “CMOS”) devices. Increasing germanium (hereinafter “Ge”)concentration in Si_(1-x)Ge_(x) to very high values, such as x>70% Ge,allows higher carrier mobilities for both electron and holes. However,Si_(1-x)Ge_(x) epitaxially grown on a single crystal Si substrate ismetastable and relaxes by generating misfit dislocations and stackingfaults when its thickness exceeds a certain value, known as the criticalthickness. This thickness decreases exponentially as x increases inSi_(1-x)Ge_(x).

Thus, there is a need for providing a method that allows for theformation of high structural quality Si_(1-x)Ge_(x)-on-insulatormaterial, in particular Si_(1-x)Ge_(x)-on-insulator materials thatcontain x>50%, that avoids the problems associated in the prior art.

SUMMARY

A layer of amorphous silicon is formed on a germanium-on-insulatorsubstrate, or a layer of germanium is formed on a silicon-on-insulatorsubstrate. An anneal is then performed which causes thermal mixing ofsilicon and germanium atoms within one of the aforementioned structuresand subsequent formation of a silicon germanium-on-insulator material.

In one aspect of the present application, various methods of forming asilicon germanium-on-insulator (SGOI) material are provided. In oneembodiment of the present application, a method of forming the SGOImaterial can include providing a structure comprising, from bottom totop, a germanium-on-insulator substrate and an amorphous silicon layer.The structure is then converted into a silicon germanium-on-insulatormaterial by annealing, wherein during the annealing silicon atoms fromthe amorphous silicon layer intermix with germanium atoms in a germaniumlayer of the germanium-on-insulator substrate to form a silicongermanium layer.

In another embodiment of the present application, a method of formingthe SGOI material may include providing a structure comprising, frombottom to top, a silicon-on-insulator substrate and a germanium layer.The structure is then converted into a silicon germanium-on-insulatormaterial by annealing, wherein during the annealing silicon atoms from asilicon layer of the silicon-on-insulator substrate intermix withgermanium atoms in the germanium layer to form a silicon germaniumlayer.

In another aspect of the present application, methods of formingsemiconductor structures are provided. In accordance with one embodimentof the present application, a method of forming the semiconductorstructure includes forming a gate structure on an active silicongermanium region of a silicon germanium-on-insulator material. Next, anamorphous silicon layer is formed on exposed surfaces of the activesilicon germanium region and surrounding the gate structure. EmbeddedSiGe source/drain regions are then formed in the active SiGe region andat a footprint of the gate structure utilizing a thermal mixing processin which silicon atoms from the amorphous silicon layer intermix withgermanium atoms in the SiGe active region to form the embedded SiGesource/drain regions.

In accordance with another embodiment of the present application,another method of forming a semiconductor structure includes forming anamorphous silicon layer portion on a surface of an active silicongermanium region of a silicon germanium-on-insulator material. A gatestructure is then formed on a surface of the amorphous silicon. Next, anembedded SiGe channel region is formed in the active SiGe region anddirectly beneath the gate structure utilizing a thermal mixing processin which silicon atoms from the amorphous silicon layer portion intermixwith germanium atoms in the SiGe active region to form the embedded SiGechannel region.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross sectional view of an exemplary semiconductor structureincluding an GeOI substrate that can be employed in accordance with anembodiment of the present application.

FIG. 2 is a cross sectional view of the exemplary semiconductorstructure of FIG. 1 after forming an amorphous Si layer on a topmostsurface of the GeOI substrate in accordance with an embodiment of thepresent application.

FIG. 3 is a cross sectional view of the exemplary semiconductorstructure of FIG. 2 after performing a thermal mixing process inaccordance with an embodiment of the present application.

FIG. 4 is a cross sectional view of the exemplary semiconductorstructure of FIG. 2 after forming a dielectric material on the amorphousSi layer in accordance with an embodiment of the present application.

FIG. 5 is a cross sectional view of the exemplary semiconductorstructure of FIG. 4 after performing a thermal mixing process inaccordance with an embodiment of the present application.

FIG. 6 is a cross sectional view of the exemplary semiconductorstructure of FIG. 5 after removing the dielectric material from thestructure in accordance with an embodiment of the present application.

FIG. 7 is a cross sectional view of an exemplary semiconductor structureincluding an SOI substrate that can be employed in accordance with anembodiment of the present application.

FIG. 8 is a cross sectional view of the exemplary semiconductorstructure of FIG. 7 after forming a germanium (Ge) layer on a topmostsurface of the SOI substrate in accordance with an embodiment of thepresent application.

FIG. 9 is a cross sectional view of the exemplary semiconductorstructure of FIG. 8 after performing a thermal mixing process inaccordance with an embodiment of the present application.

FIG. 10 is a cross sectional view of the exemplary semiconductorstructure of FIG. 8 after forming a dielectric material on the Ge layerin accordance with an embodiment of the present application.

FIG. 11 is a cross sectional view of the exemplary semiconductorstructure of FIG. 10 after performing a thermal mixing process inaccordance with an embodiment of the present application.

FIG. 12 is a cross sectional view of the exemplary semiconductorstructure of FIG. 11 after removing the dielectric material from thestructure in accordance with an embodiment of the present application.

FIG. 13 is a cross sectional view of the exemplary semiconductorstructure of FIG. 8 after forming an amorphous region at an interfacebetween the Ge layer and a silicon layer of the SOI substrate inaccordance with an embodiment of the present application.

FIG. 14 is a cross sectional view of the exemplary semiconductorstructure of FIG. 13 after performing a thermal mixing process inaccordance with an embodiment of the present application.

FIG. 15 is a cross sectional view of the exemplary semiconductorstructure of FIG. 13 after forming a dielectric material on the Ge layerin accordance with an embodiment of the present application.

FIG. 16 is a cross sectional view of the exemplary semiconductorstructure of FIG. 15 after performing a thermal mixing process inaccordance with an embodiment of the present application.

FIG. 17 is a cross sectional view of the exemplary semiconductorstructure of FIG. 16 after removing the dielectric material from thestructure in accordance with an embodiment of the present application.

FIG. 18 is a cross sectional view of the exemplary semiconductorstructure of FIG. 2 after forming dielectric structures within theamorphous Si layer and the Ge layer of the GeOI substrate in accordancewith an embodiment of the present application.

FIG. 19 is a cross sectional view of the exemplary semiconductorstructure of FIG. 18 after performing a thermal mixing process inaccordance with an embodiment of the present application.

FIG. 20 is a cross sectional view of an exemplary semiconductorstructure including a gate structure located on an active silicongermanium (SiGe) region of an SGOI substrate in accordance with anembodiment of the present application.

FIG. 21 is a cross sectional view of the exemplary semiconductorstructure of FIG. 20 after formation of a gate dielectric spacer.

FIG. 22 is a cross sectional view of the exemplary semiconductorstructure of FIG. 21 after forming an amorphous Si layer.

FIG. 23 is a cross sectional view of the exemplary semiconductorstructure of FIG. 22 after forming embedded SiGe source/drain regions inthe active SiGe region and at a footprint of the gate structureutilizing a thermal mixing process in accordance with an embodiment ofthe present application.

FIG. 24 is a cross sectional view of an exemplary semiconductorstructure including an amorphous Si layer portion on an active SiGeregion of an SGOI substrate in accordance with an embodiment of thepresent application.

FIG. 25 is a cross sectional view of the exemplary semiconductorstructure of FIG. 24 after formation of a gate structure on theamorphous Si layer portion and formation of a gate dielectric spacer.

FIG. 26 is a cross sectional view of the exemplary semiconductorstructure of FIG. 25 after forming an embedded SiGe channel region inthe active SiGe region and directly beneath the gate structure utilizinga thermal mixing process in accordance with an embodiment of the presentapplication.

DETAILED DESCRIPTION

The present application will now be described in greater detail byreferring to the following discussion and drawings that accompany thepresent application. It is noted that the drawings of the presentapplication are provided for illustrative purposes only and, as such,the drawings are not drawn to scale. It is also noted that like andcorresponding elements are referred to by like reference numerals.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide an understanding ofthe various embodiments of the present application. However, it will beappreciated by one of ordinary skill in the art that the variousembodiments of the present application may be practiced without thesespecific details. In other instances, well-known structures orprocessing steps have not been described in detail in order to avoidobscuring the present application.

Referring first to FIG. 1, there is illustrated an exemplarysemiconductor structure including an GeOI substrate 10 that can beemployed in accordance with an embodiment of the present application.The GeOI substrate 10 that can be employed in the present applicationincludes, from bottom to top, a handle substrate 12, an insulator layer14, and a germanium layer 16. The handle substrate 12 providesmechanical support for the insulator layer 14 and the germanium layer16.

In one embodiment of the present application, the handle substrate 12 ofthe GeOI substrate 10 may comprise any semiconductor material. The term“semiconductor” as used throughout the present application denotes amaterial that has an electrical conductivity value between a conductor,such as copper, and an insulator such as, silicon dioxide. Thesemiconductor material that may provide the handle substrate 12 of theGeOI substrate 10 includes, for example, doped and undoped Si, doped andundoped Ge or doped and undoped SiGe. Multilayers of these semiconductormaterials can also be used as the semiconductor material that provideshandle substrate 12. In some embodiments, the handle substrate 12 andthe germanium layer 16 are both comprised of germanium. In someembodiments of the present application, the handle substrate 12 is anon-semiconductor material such as, for example, a dielectric materialand/or a conductor. In yet other embodiments, the handle substrate 12may be omitted.

In some embodiments, the handle substrate 12 and the germanium layer 16may have a same crystal orientation. In other embodiments, the handlesubstrate 12 and the germanium layer 16 may have different crystalorientations. For example, the crystal orientation of the handlesubstrate 12 and/or the germanium layer 16 may be {100}, {110}, or{111}. Other crystallographic orientations besides those specificallymentioned can also be used in the present application. The handlesubstrate 12 and/or the germanium layer 16 of the GeOI substrate 10 maybe a single crystalline semiconductor material, a polycrystallinematerial, or an amorphous material. Typically, at least the germaniumlayer 16 is a single crystalline semiconductor material.

The insulator layer 14 of the GeOI substrate 10 may be a crystalline ornon-crystalline oxide or nitride. In one embodiment, the insulator layer14 is an oxide such as, for example, silicon dioxide. The germaniumlayer 16 of the GeOI substrate 10 consists of elemental, i.e.,non-alloyed, germanium.

The GeOI substrate 10 may be formed utilizing standard processesincluding for example, layer transfer. Typically, a layer transferprocess is employed in providing the GeOI substrate 10. In suchinstances, a first semiconductor wafer including at least a layer ofgermanium is bonded to a second semiconductor wafer that includes theinsulator layer 14 and the handle substrate 12. In some embodiments, abulk germanium substrate may be employed as the first wafer. In otherembodiments, the first wafer includes a germanium layer formed by adeposition process such, as for example, epitaxial growth, on a surfaceof a sacrificial semiconductor substrate. In some embodiments, thesacrificial substrate may include silicon, and a graded SiGeintermediate layer can be formed between the sacrificial substrate andthe overlying germanium layer 16. Various material removal processes canbe used to remove the sacrificial substrate and the graded SiGeintermediate layer after bonding. When a layer transfer process isemployed, an optional thinning step may follow the bonding of the firstand second wafers together. The optional thinning step reduces thethickness of the germanium layer 16 to a layer having a thickness thatis more desirable.

In one example, the thickness of the germanium layer 16 of the GeOIsubstrate 10 can be from 10 nm to 200 nm. In another example, thethickness of the germanium layer 16 of the GeOI substrate 10 can be from50 nm to 70 nm. Other thicknesses that are lesser than or greater thanthe aforementioned thicknesses ranges may also be employed as thethickness of the germanium layer 16. For example, and when an ETGeOI(extremely thin germanium-on-insulator) substrate is employed, thegermanium layer 16 can have a thickness of less than 10 nm. If thethickness of the germanium layer 16 layer is not within a desired range,a thinning step such as, for example, planarization or etching can beused to reduce the thickness of the germanium layer 16 to a value withina desired thickness range. The insulator layer 14 of the GeOI substrate10 typically has a thickness from 1 nm to 200 nm, with a thickness from100 nm to 150 nm being more typical. Other thicknesses that are lesserthan or greater than the aforementioned thickness ranges can also beemployed as the thickness of the insulator layer 14. The thickness ofthe handle substrate 12 of the GeOI substrate 10 is inconsequential tothe present application.

Referring now to FIG. 2, there is illustrated the exemplarysemiconductor structure of FIG. 1 after forming an amorphous Si layer 18on a topmost surface of the GeOI substrate 10 in accordance with anembodiment of the present application. As is shown, the amorphous Silayer 18 is a contiguous layer that spans the entirety of the topmostsurface of the GeOI substrate 10. As is also shown, the amorphous Silayer 18 is formed on a surface of the germanium layer 16 of the GeOIsubstrate 10. The term “amorphous Si” is used throughout the presentapplication to denote a non-crystalline allotropic form of silicon.

The amorphous Si layer 18 can be formed utilizing a deposition processincluding, for example, physical vapor deposition (PVD; also referred toas sputter deposition), chemical vapor deposition (CVD), rapid thermalchemical vapor deposition (RTCVD), plasma enhanced chemical vapordeposition (PECVD), or inductively coupled plasma chemical vapordeposition (ICP CVD). In some embodiments, hydrogen may be introducedduring the deposition process forming a hydrogenated amorphous Si layer.The amorphous Si layer 18 can have a thickness from 10 nm to 200 nm.Other thickness that are lesser than or greater than the aforementionedthickness range can also be employed as the thickness of the amorphousSi layer 18.

Referring now to FIG. 3, there is illustrated the exemplarysemiconductor structure of FIG. 2 after performing a thermal mixingprocess in accordance with an embodiment of the present application.During thermal mixing, the amorphous Si layer 18 and the underlyinggermanium layer 16 are converted into a silicon germanium layer 20.Notably, and during thermal mixing, silicon atoms from the amorphoussilicon layer 18 diffuse and intermix with germanium atoms in thegermanium layer 16 of the germanium-on-insulator substrate GeOI to formsilicon germanium layer 20. Thus, a silicon germanium-on-insulator(i.e., SGOI) material 22 including, from bottom to top, the handlesubstrate 12, the insulator layer 14 and the silicon germanium layer 20,is formed. Typically, and as shown, the amorphous Si layer 18 and thegermanium layer 16 are completely consumed during the thermal mixingprocess. In some embodiments, a portion of the amorphous Si layer 18 mayremain and can be removed by utilizing a chemical removal process.

In accordance with the present application, thermal mixing is performedin this embodiment of the present application by annealing in an inertambient. Examples of inert ambients that can be used during the annealinclude helium (He), argon (Ar), neon (Ne), nitrogen (N₂) or anymixtures thereof. In one embodiment, the anneal is performed in N₂. Asingle anneal may be performed or multiple anneals (in the same ordifferent inert ambient) may be performed. In one embodiment of thepresent application, the anneal may be performed at a temperature from600° C. to 900° C. In some embodiments, the anneal may be performed at aconstant rate. In other embodiments, the anneal may be performed adifferent, variable rates. In yet other embodiments, the anneal may beperformed utilizing a series of ramp up cycles and soak cycles, asdesired.

In some embodiments, the anneal may be performed in a same reactorchamber (i.e., in-situ) as used to deposit the amorphous Si layer 18. Inother embodiments, the anneal may be performed in a different reactorchamber (i.e., ex-situ) from that used to deposit the amorphous Si layer18.

The resultant silicon germanium layer 20 that forms may have a germaniumcontent from 5 atomic percent germanium to 90 atomic percent germanium.In one embodiment of the present application, the silicon germaniumlayer 20 that forms may have a germanium content of greater than 50atomic percent germanium to 90 atomic percent germanium. The germaniumcontent within the silicon germanium layer 20 can be controlled in thepresent application by the thickness of the amorphous Si layer 18,and/or the thickness of the germanium layer 16 and/or the conditions ofthe anneal used to perform the thermal mixing. For example, the thickerthe amorphous Si layer 18 and/or the thinner the germanium layer 16, thelower the germanium content is within the silicon germanium layer 20that is formed. The amorphous Si layer 18 also aides in preventingoxidation of the germanium layer 16 during the anneal. In the presentapplication, X-ray, Raman, SIMS, and TEM were used to verify Sidiffusion, and conversion of the GeOI substrate 10 into the SGOIsubstrate 22.

Referring now to FIG. 4, there is illustrated the exemplarysemiconductor structure of FIG. 2 after forming a dielectric material 24on the amorphous Si layer 18 in accordance with an embodiment of thepresent application. The dielectric material 24 is a contiguousdielectric that spans the entirety of the amorphous Si layer 18. Thedielectric material 24 includes any insulator material including, forexample, silicon dioxide, silicon nitride and/or silicon oxynitride.Other examples of insulators that can be employed as the dielectricmaterial 24 include for example, a dielectric metal oxide such as, forexample, HfO₂, ZrO₂, La₂O₃, Al₂O₃, TiO₂, SrTiO₃, LaAlO₃, Y₂O₃,HfO_(x)N_(y), ZrO_(x)N_(y), La₂O_(x)N_(y), Al₂O_(x)N_(y), TiO_(x)N_(y),SrTiO_(x)N_(y), LaAlO_(x)N_(y), Y₂O_(x)N_(y), SiON, SiN_(x), a silicatethereof, and an alloy thereof. Each value of x is independently from 0.5to 3 and each value of y is independently from 0 to 2. In someembodiments, a multilayered dielectric structure comprising differentdielectric materials, e.g., silicon dioxide, and a dielectric metaloxide, can be formed and used as the dielectric material 24.

In some embodiments of the present application, the dielectric material24 can be formed by a deposition technique such as, for example,chemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD), physical vapor deposition (PVD), sputtering, oratomic layer deposition. In another embodiment of the presentapplication, the dielectric material 24 can be formed by a thermalgrowth technique such as, for example, thermal oxidation and/or thermalnitridation. In yet a further embodiment of the present application, acombination of a deposition and thermal growth may be used in forming amultilayered dielectric material 24 structure.

In one embodiment of the present application, the dielectric material 24can have a thickness in a range from 10 nm to 100 nm. Other thicknessesthat are lesser than or greater than the aforementioned thickness rangecan also be employed for the thickness of the dielectric material 24.

Referring now to FIG. 5, there is illustrated the exemplarysemiconductor structure of FIG. 4 after performing a thermal mixingprocess in accordance with an embodiment of the present application. Thethermal mixing that is employed in this embodiment of the presentapplication is an anneal as described in the previous embodiment of thepresent application; the anneal ambient and conditions described aboveare applicable here for this embodiment of the present application aswell.

The thermal mixing converts the GeOI substrate 10 into a silicongermanium-on-insulator (i.e., SGOI) material 22 including, from bottomto top, the handle substrate 12, the insulator layer 14 and the silicongermanium layer 20. Typically, and as shown, the amorphous Si layer 18and the germanium layer 16 are completely consumed during the thermalmixing process. The dielectric material 24 remains and is present atopthe silicon germanium layer 20 of the SGOI material 22. In someembodiments, a portion of the amorphous Si layer 18 can remain betweenthe dielectric material 24 and the now formed silicon germanium layer20.

Referring now to FIG. 6, there is illustrated the exemplarysemiconductor structure of FIG. 5 after removing the dielectric material24 from the structure (i.e., the SGOI material 22) in accordance with anembodiment of the present application. In some embodiments (not shown),the entirety of the dielectric material 24 may remain atop the SGOImaterial 22. In other embodiments, portions of the dielectric material24 may be removed to provide either a dielectric material having areduced thickness as compared to the originally deposited dielectricmaterial 24, or patterned dielectric material portions.

In one embodiment of the present application, the dielectric material 24can be entirely or partially removed utilizing chemical mechanicalplanarization, grinding and/or chemical etching. In cases in whichpatterned dielectric material portions are formed, lithography andetching can be used to pattern the dielectric material 24.

Referring now to FIG. 7, there is illustrated an exemplary semiconductorstructure including an SOI substrate 30 that can be employed inaccordance with an embodiment of the present application. The SOIsubstrate 30 that can be employed in the present application includes,from bottom to top, a handle substrate 32, an insulator layer 34, and asilicon layer 36. The handle substrate 32 provides mechanical supportfor the insulator layer 34 and the silicon layer 36.

The handle substrate 32 of the SOI substrate 30 may comprise one of thesemiconductor materials mentioned above for handle substrate 12. In someembodiments, the handle substrate 32 and the silicon layer 36 are bothcomprised of silicon. In some embodiments of the present application,the handle substrate 32 is a non-semiconductor material such as, forexample, a dielectric material and/or a conductor. In yet otherembodiments, the handle substrate 32 may be omitted.

In some embodiments, the handle substrate 32 and the silicon layer 36may have a same crystal orientation. In other embodiments, the handlesubstrate 32 and the silicon layer 36 may have different crystalorientations. For example, the crystal orientation of the handlesubstrate 32 and/or the silicon layer 36 may be {100}, {110}, or {111}.Other crystallographic orientations besides those specifically mentionedcan also be used in the present application. The handle substrate 32and/or the silicon layer 36 of the SOI substrate 30 may be a singlecrystalline semiconductor material, a polycrystalline material, or anamorphous material. Typically, at least the silicon layer 36 is a singlecrystalline semiconductor material.

The insulator layer 34 of the SOI substrate 30 may be a crystalline ornon-crystalline oxide or nitride. In one embodiment, the insulator layer34 is an oxide such as, for example, silicon dioxide. The silicon layer36 of the SOI substrate 30 consists of elemental, i.e., non-alloyed,silicon.

The SOI substrate 30 may be formed utilizing standard processesincluding for example, layer transfer. Typically, a layer transferprocess is employed in providing the SOI substrate 30. In suchinstances, a first semiconductor wafer including at least a layer ofsilicon is bonded to a second semiconductor wafer that includes theinsulator layer 34 and the handle substrate 32. In some embodiments, abulk silicon substrate may be employed as the first wafer. In otherembodiments, the first wafer includes a silicon layer formed by adeposition process such, as for example, epitaxial growth, on a surfaceof a sacrificial semiconductor substrate. In some embodiments, thesacrificial substrate may include silicon, and a graded SiGeintermediate layer can be formed between the sacrificial substrate andthe overlying silicon layer 36. The sacrificial substrate and the gradedSiGe intermediate layer can be removed after bonding. When a layertransfer process is employed, an optional thinning step may follow thebonding of the first and second wafers together. The optional thinningstep reduces the thickness of the silicon layer 36 to a layer having athickness that is more desirable.

In one example, the thickness of the silicon layer 36 of the SOIsubstrate 30 can be from 10 nm to 100 nm. In another example, thethickness of the silicon layer 36 of the SOI substrate 30 can be from 50nm to 70 nm. Other thicknesses that are lesser than or greater than theaforementioned thicknesses ranges may also be employed in the presentapplication. For example, and when an ETSOI (extremely thinsilicon-on-insulator) substrate is employed, the silicon layer 36 canhave a thickness of less than 10 nm. If the thickness of the siliconlayer 36 layer is not within a desired range, a thinning step such as,for example, planarization or etching can be used to reduce thethickness of the silicon layer 36 to a value within a desired thicknessrange. The insulator layer 34 of the SOI substrate 30 typically has athickness from 1 nm to 200 nm, with a thickness from 100 nm to 150 nmbeing more typical. Other thicknesses that are lesser than or greaterthan the aforementioned thickness ranges can also be employed as thethickness of the insulator layer 34. The thickness of the handlesubstrate 32 of the SOI substrate 30 is inconsequential to the presentapplication.

Referring now to FIG. 8, there is illustrated the exemplarysemiconductor structure of FIG. 7 after forming a germanium (Ge) layer38 on a topmost surface of the SOI substrate 30 in accordance with anembodiment of the present application. As is shown, the Ge layer 38 is acontiguous layer that spans the entirety of the topmost surface of theSOI substrate 30. As is also shown, the Ge layer 38 is formed on asurface of the silicon layer 36 of the SOI substrate 30.

The Ge layer 38 can be formed utilizing a deposition process including,for example, epitaxial growth. The terms “epitaxial growth and/ordeposition” and “epitaxially formed and/or grown” mean the growth of asemiconductor material on a deposition surface of a semiconductormaterial, in which the semiconductor material being grown has the samecrystalline characteristics as the semiconductor material of thedeposition surface. In an epitaxial deposition process, the chemicalreactants provided by the source gases are controlled and the systemparameters are set so that the depositing atoms arrive at the depositionsurface of the semiconductor substrate with sufficient energy to movearound on the surface and orient themselves to the crystal arrangementof the atoms of the deposition surface. Therefore, an epitaxialsemiconductor material has the same crystalline characteristics as thedeposition surface on which it is formed. For example, an epitaxialsemiconductor material deposited on a {100} crystal surface will take ona {100} orientation. Thus, and in the present embodiment, the Ge layer38 has an epitaxial relationship, i.e., same crystal orientation, asthat of the surface of the Si layer 36.

Examples of various epitaxial growth process that are suitable for usein forming the Ge layer 38 of the present application include, e.g.,rapid pressure chemical vapor deposition (RPCVD), low-energy plasmadeposition (LEPD), ultra-high vacuum chemical vapor deposition (UHVCVD),atmospheric pressure chemical vapor deposition (APCVD) or molecular beamepitaxy (MBE). The temperature for epitaxial deposition process forforming the Ge layer 38 typically ranges from 550° C. to 900° C.Although higher temperature typically results in faster deposition, thefaster deposition may result in crystal defects and film cracking.

A number of different germanium source gases which are well known tothose skilled in the art may be used for the deposition of the Ge layer38. Carrier gases like hydrogen, nitrogen, helium and argon can be usedduring the epitaxial growth process. In some embodiments, hydrogen maybe introduced during the deposition process forming a hydrogenated Gelayer. The Ge layer 38 can have a thickness from 10 nm to 200 nm. Otherthickness that are lesser than or greater than the aforementionedthickness range can also be employed as the thickness of the Ge layer38.

Referring now to FIG. 9, there is illustrated the exemplarysemiconductor structure of FIG. 8 after performing a thermal mixingprocess in accordance with an embodiment of the present application.During thermal mixing, the Ge layer 38 and the underlying Si layer 36are converted into a silicon germanium layer 40; intermixing occurs atthe interface between the Ge layer 38 and the Si layer 38. Notably, andduring thermal mixing, silicon atoms from the Si layer 36 diffuse andintermix with germanium atoms in the Ge layer 38 to form silicongermanium layer 40. Thus, a silicon germanium-on-insulator (i.e., SGOI)material 42 including, from bottom to top, the handle substrate 32, theinsulator layer 34 and the silicon germanium layer 42, is formed.Typically, and as shown, the Si layer 36 and the Ge layer 38 arecompletely consumed during the thermal mixing process. In someembodiments, a portion of the Ge layer 38 can remain atop the now formedsilicon germanium layer 42. In such an embodiment, any remaining Gelayer 38 can be removed utilizing chemical mechanical planarization,grinding and/or chemical (wet or dry) etching. In some embodiments, theremaining Ge layer 38 can be left atop the now formed silicon germaniumlayer 42.

In accordance with the present application, thermal mixing is performedin this embodiment of the present application by annealing in hydrogen(H₂). In some embodiments, the hydrogen may be admixed with an inertambient such as, for example, helium (He), argon (Ar), neon (Ne),nitrogen (N₂) or any mixtures thereof; in such an embodiment thehydrogen is present in a concentration up to 10 vol. %, the remainder upto 100 vol. % being one of the inert ambients mentioned above. In oneembodiment, the anneal is performed in H₂ only. A single anneal may beperformed or multiple anneals (in the same or different H₂ ambient) maybe performed. In one embodiment of the present application, the annealmay be performed at a temperature from 600° C. to 900° C. In someembodiments, the anneal may be performed at a constant rate. In otherembodiments, the anneal may be performed a different, variable rates. Inyet other embodiments, the anneal may be performed utilizing a series oframp up cycles and soak cycles, as desired.

In some embodiments, the anneal may be performed in a same reactorchamber (i.e., in-situ) as used to deposit the Ge layer 38. In otherembodiments, the anneal may be performed in a different reactor chamber(i.e., ex-situ) from that used to deposit the Ge layer 38.

The resultant silicon germanium layer 40 that forms may have a germaniumcontent from 5 atomic percent germanium to 90 atomic percent germanium.In one embodiment of the present application, the silicon germaniumlayer 40 that forms may have a germanium content of greater than 50atomic percent germanium to 90 atomic percent germanium. The germaniumcontent within the silicon germanium layer 40 can be controlled in thepresent application by the thickness of the Si layer 36, and/or thethickness of the Ge layer 38 and/or the conditions of the anneal used toperform the thermal mixing. For example, the thicker the Si layer 36and/or the thinner the Ge layer 38, the lower the germanium content iswithin the silicon germanium layer 40 that is formed. In the presentapplication, X-ray, Raman, SIMS, and TEM were used to verify Sidiffusion, and conversion of the SOI substrate 30 into the SGOIsubstrate 42.

Referring now to FIG. 10, there is illustrated the exemplarysemiconductor structure of FIG. 8 after forming a dielectric material 44on the Ge layer 38 in accordance with an embodiment of the presentapplication. The dielectric material 44 that is employed in thisembodiment of the present application may include one of the insulatorsmentioned above for dielectric material 24. Also, the dielectricmaterial 44 may be formed by, and have a thickness within a range, asmentioned above for dielectric material 24.

Referring now to FIG. 11, there is illustrated the exemplarysemiconductor structure of FIG. 10 after performing a thermal mixingprocess in accordance with an embodiment of the present application. Thethermal mixing process used in this embodiment of the presentapplication is the same as that described above in providing thestructure shown in FIG. 9; the anneal ambient and conditions describedabove in regard to providing the structure shown in FIG. 9 areapplicable here for this embodiment of the present application as well.

The thermal mixing converts the SOI substrate 30 and the Ge layer 38into a silicon germanium-on-insulator (i.e., SGOI) material 42including, from bottom to top, the handle substrate 32, the insulatorlayer 34 and the silicon germanium layer 40. Typically, and as shown,the Si layer 36 and the Ge layer 38 are completely consumed during thethermal mixing process. In some embodiments, a remaining portion of theGe layer 38 (not shown) may be located between the dielectric material44 and the silicon germanium layer 40. The dielectric material 44remains and is present atop the silicon germanium layer 40 of the SGOImaterial 42.

Referring now to FIG. 12, there is illustrated the exemplarysemiconductor structure of FIG. 11 after removing the dielectricmaterial 44 from the structure in accordance with an embodiment of thepresent application. The dielectric material 44 can be removed utilizingchemical mechanical planarization, grinding and/or chemical etching. Inembodiments in which a remaining portion of Ge layer 38 is present, theremaining portion of Ge layer 38 can be removed utilizing chemicalmechanical planarization, grinding and/or chemical etching.

Referring now to FIG. 13, there is illustrated the exemplarysemiconductor structure of FIG. 8 after forming an amorphous region 46at an interface between the Ge layer 38 and the SOI substrate 30 (i.e.,the Si layer 36) in accordance with an embodiment of the presentapplication. In the embodiment that is illustrated, the amorphous region46 is continuously present between the Ge layer 38 and the Si layer 36.

The amorphous region 46 is a region that lacks any well defined crystalstructure. Moreover, the amorphous region 46 is a region in whichcrystal damage has been introduced into the structure by utilizing oneor more amorphization ion implantation processes. The one or moreamorphization ion implantation processes includes ion implanting anamorphizing ion into the structure. The amorphizing ion that can beemployed in the present application in providing the amorphous region 46includes any ion such as Si or Ge. The one or more amorphization ionimplantation processes may be performed at room temperature (i.e., from20° C. to 40° C.), or temperatures below room temperature may beemployed. The conditions for the one or more amorphization ionimplantation process are selected to form the amorphous region 44 at theinterface between the Si layer 36 and the Ge layer 38.

Referring now to FIG. 14, there is illustrated the exemplarysemiconductor structure of FIG. 13 after performing a thermal mixingprocess in accordance with an embodiment of the present application. Thethermal mixing process used in this embodiment of the presentapplication is the same as that described above in providing thestructure shown in FIG. 9; the anneal ambient and conditions describedabove in regard to providing the structure shown in FIG. 9 areapplicable here for this embodiment of the present application as well.

The thermal mixing converts the SOI substrate 30 and the Ge layer 38into a silicon germanium-on-insulator (i.e., SGOI) material 42including, from bottom to top, the handle substrate 32, the insulatorlayer 34 and a silicon germanium layer 40. Typically, and as shown, theSi layer 36 and the Ge layer 38 are completely consumed during thethermal mixing process. In some embodiments, a remaining portion of theGe layer 38 (not shown) may be located atop the silicon germanium layer40. During the thermal mixing process, the amorphous region 46 isrecrystallized.

Referring now to FIG. 15, there is shown the exemplary semiconductorstructure of FIG. 13 after forming a dielectric material 44 on the Gelayer 38 in accordance with an embodiment of the present application.The dielectric material 44 that is employed in this embodiment of thepresent application may include one of the insulators mentioned abovefor dielectric material 24. Also, the dielectric material 44 may beformed by, and have a thickness within a range, as mentioned above fordielectric material 24.

Referring now to FIG. 16, there is illustrated the exemplarysemiconductor structure of FIG. 16 after performing a thermal mixingprocess in accordance with an embodiment of the present application. Thethermal mixing process used in this embodiment of the presentapplication is the same as that described above in providing thestructure shown in FIG. 9; the anneal ambient and conditions describedabove in regard to providing the structure shown in FIG. 9 areapplicable here for this embodiment of the present application as well.

The thermal mixing converts the SOI substrate 30 and the Ge layer 38into a silicon germanium-on-insulator (i.e., SGOI) material 42including, from bottom to top, the handle substrate 32, the insulatorlayer 34 and the silicon germanium layer 40. Typically, and as shown,the Si layer 36 and the Ge layer 38 are completely consumed during thethermal mixing process. In some embodiments, a remaining portion of theGe layer 38 (not shown) may be located between the dielectric material44 and the silicon germanium layer 40. The dielectric material 44remains and is present atop the silicon germanium layer 40 of the SGOImaterial 42. During the thermal mixing process, the amorphous region 46is recrystallized.

Referring now to FIG. 17, there is illustrated the exemplarysemiconductor structure of FIG. 16 after removing the dielectricmaterial 44 from the structure in accordance with an embodiment of thepresent application. The dielectric material 44 can be removed utilizingchemical mechanical planarization, grinding and/or chemical etching. Inembodiments in which a remaining portion of Ge layer 38 is present, theremaining portion of Ge layer 38 can be removed utilizing chemicalmechanical planarization, grinding and/or chemical etching.

Referring now to FIG. 18, there is illustrated the exemplarysemiconductor structure of FIG. 1 after forming dielectric structures 50within the amorphous Si layer 18 and the Ge layer 16 of the GeOIsubstrate 10 in accordance with an embodiment of the presentapplication. In the drawing, the remaining portions of the amorphous Silayer 18 are labeled as 18P and can be referred to hereinafter asamorphous Si portions 18P. In the drawing, the remaining portions of theGe layer 16 are labeled as 16P and can be referred to hereinafter asgermanium portions 16P.

The number of dielectric structures 50 that can be formed is not limitedto two as shown in FIG. 18. Instead, a single dielectric structure 50can be formed, or greater than two dielectric structures 50 can beformed. Each dielectric structure 50 that is formed has a bottommostsurface in contact with a topmost surface of the insulator layer 14.Each dielectric structure 50 that is formed has sidewall surfaces thatcontact sidewall surfaces of an abutting germanium portion 16P and anabutting amorphous Si portion 18P. Each dielectric structure 50 can havea topmost surface that is coplanar with a topmost surface of theamorphous Si portions 18P. In some embodiments, the topmost surface ofeach dielectric structure 50 may extend above or below the topmostsurface of the amorphous Si portions 18P.

Each dielectric structure 50 can be formed by first forming a trenchthrough the amorphous Si layer 18 and through the Ge layer 16, stoppingon a topmost surface of the insulator layer 14. The trench can be formedby lithography and anisotropic etching. A single etch or multipleetching steps may be used in providing the trench. Once the trench isformed, the trench is filled with a trench dielectric material such as,for example, silicon dioxide. A planarization process may follow thetrench dielectric fill.

Referring now to FIG. 19, there is illustrated the exemplarysemiconductor structure of FIG. 18 after performing a thermal mixingprocess in accordance with an embodiment of the present application.During thermal mixing, the amorphous Si portions 18P and the underlyinggermanium portions 16P are converted into a silicon germanium portions20P. Notably, and during thermal mixing silicon atoms from the amorphoussilicon portions 18P diffuse and intermix with germanium atoms in thegermanium portions 16P of the germanium-on-insulator substrate GeOI toform silicon germanium portions 20P. Thus, a silicongermanium-on-insulator (i.e., SGOI) material 22 including, from bottomto top, the handle substrate 12, the insulator layer 14 and silicongermanium portions 20P, is formed. Typically, and as shown, theamorphous Si portions 18P and the germanium portions 16P are completelyconsumed during the thermal mixing process. In some embodiments, anupper portion of the amorphous Si portion 18P can remain and be removedduring a subsequently performed material removal process. As is alsoshown, each silicon germanium portion 20P is isolated from its nearestneighboring silicon germanium portion 20P by a dielectric structure 50.

In accordance with the present application, thermal mixing is performedin this embodiment of the present application by annealing utilizing theconditions and ambient mentioned above in providing the structure shownin FIG. 3 of the present application. Each silicon germanium portion 20Pthat is formed is similar to the silicon germanium layer 20 formed inFIG. 3. In some embodiments, and following the thermal mixing process, aplanarization process can be performed to provide the planar structureshown in FIG. 19. In some embodiments (not shown), the topmost surfaceof each dielectric structure 50 may extend above the topmost surface ofeach silicon germanium portion 20P.

Although not shown, it is possible to form a dielectric material acrossthe structure shown in FIG. 18 prior to performing the thermal mixingprocess. The dielectric material can be removed after the thermal mixingis performed as also described hereinabove.

Referring now to FIG. 20, there is illustrated an exemplarysemiconductor structure including, a gate structure 70 located on anactive SiGe region 66 of a SGOI substrate 60 in accordance with anembodiment of the present application. In addition to the active SiGeregion 66, the SGOI substrate 60 also includes a handle substrate 62 andan insulator layer 64. Handle substrate 62 includes one of the materialsmentioned above for handle substrate 12. Insulator layer 64 includes oneof the insulator materials mentioned above for insulator layer 14. Inthe present embodiments, active SiGe region 66 includes a patternedsilicon germanium layer. In some embodiments, the active SiGe region 66may comprise a non-patterned silicon germanium layer. Although a singleactive SiGe region 66 is described and illustrated, a plurality ofactive SiGe regions can be present atop the insulator layer 64.

The silicon germanium layer that provides the active silicon germaniumregion 66 can be formed utilizing any of the various embodiments of thepresent application including the one described in FIGS. 18 and 19 ofthe present application. Element 68 represents dielectric structures. Insome embodiments, the dielectric structures 68 are formed prior toformation of the silicon germanium layer that provides the activesilicon region 66 (as shown, for example, in FIGS. 18 and 19 above). Inother embodiments, the silicon germanium layer that provides the activesilicon germanium region 66 is formed first, and then the dielectricstructures are formed by forming a trench (by lithography and etching)and filling the trench with a trench dielectric material.

In some embodiments (not shown), the active silicon germanium region 66can be processed into a fin structure or a nanowire structure utilizingprocesses techniques well known to those skilled in the art. When a finstructure or nanowire structure is formed, the subsequently formed gatestructure would straddle the fin structure or the nanowire structure.

In some embodiments of the present application, the gate structure 70can be a functional gate structure. By “functional gate structure” it ismeant a permanent gate structure used to control output current (i.e.,flow of carriers in the channel of a semiconductor device throughelectrical or magnetic fields. In other embodiments, the gate structure70 can be a sacrificial gate structure. By “sacrificial gate structure”it is meant a material or materials that serves (or serve) as aplaceholder structure for a functional gate structure to be subsequentlyformed.

In embodiments in which the gate structure 70 is a functional gatestructure, the gate structure includes, from bottom to top, a gatedielectric portion 72, a gate conductor portion 70, and a gate capportion 76. In some embodiments, the gate cap portion 76 may be omitted.

The gate dielectric portion 72 includes a gate dielectric material. Inone embodiment, the gate dielectric material that provides the gatedielectric portion 72 may be a semiconductor oxide, a semiconductornitride, and/or a semiconductor oxynitride. In one example, the gatedielectric material that can be used in providing the gate dielectricportion 72 can be composed of silicon dioxide, silicon nitride and/orsilicon oxynitride. In another embodiment of the present application,the gate dielectric material that can be used in providing the gatedielectric portion 72 may include at least a dielectric metal oxide.Exemplary dielectric metal oxides that can be used as the gatedielectric material that provides gate dielectric portion 72 include,but are not limited to, HfO₂, ZrO₂, La₂O₃, Al₂O₃, TiO₂, SrTiO₃, LaAlO₃,Y₂O₃, HfO_(x)N_(y), ZrO_(x)N_(y), La₂O_(x)N_(y), Al₂O_(x)N_(y),TiO_(x)N_(y), SrTiO_(x)N_(y), LaAlO_(x)N_(y), Y₂O_(x)N_(y), SiON,SiN_(x), a silicate thereof, and an alloy thereof. Each value of x isindependently from 0.5 to 3 and each value of y is independently from 0to 2. In some embodiments, a multilayered gate dielectric structurecomprising different gate dielectric materials, e.g., silicon dioxide,and a dielectric metal oxide can be formed and used as the gatedielectric material that provides the gate dielectric portion 72.

In some embodiments of the present application, the gate dielectricmaterial that provides the gate dielectric portion 72 can be formed by adeposition technique such as, for example, chemical vapor deposition(CVD), plasma enhanced chemical vapor deposition (PECVD), physical vapordeposition (PVD), sputtering, or atomic layer deposition. In anotherembodiment of the present application, the gate dielectric material thatprovides the gate dielectric portion 72 can be formed by a thermalgrowth technique such as, for example, thermal oxidation and/or thermalnitridation. In yet a further embodiment of the present application, acombination of a deposition and thermal growth may be used in forming amultilayered gate dielectric structure that provides the gate dielectricportion 72.

In one embodiment of the present application, the gate dielectricmaterial that provides the gate dielectric portion 72 can have athickness in a range from 1 nm to 10 nm. Other thicknesses that arelesser than or greater than the aforementioned thickness range can alsobe employed for the gate dielectric material that provides the gatedielectric portion 72.

The gate conductor portion 74 includes a gate conductor material. In oneembodiment of the present application, the gate conductor material thatprovides the gate conductor portion 74 can be composed of dopedpolysilicon, doped silicon germanium, an elemental metal (e.g.,tungsten, titanium, tantalum, aluminum, nickel, ruthenium, palladium andplatinum), an alloy of at least two elemental metals, an elemental metalnitride (e.g., tungsten nitride, aluminum nitride, and titaniumnitride), or multilayered combinations thereof. In one embodiment, anentirety of the gate conductor material that provides the gate conductorportion 74 is comprised of a doped polysilicon or doped polysilicongermanium. In another embodiment, a lower portion of the gate conductormaterial that provides the gate conductor portion 74 is comprised aconductive material other than doped polysilicon or doped polysilicongermanium, and an upper portion of the gate conductor material thatprovides the gate conductor portion 74 is comprised of doped polysiliconor doped silicon germanium.

The gate conductor material that provides the gate conductor portion 74can be formed utilizing a deposition process including, for example,chemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD), physical vapor deposition (PVD), sputtering, atomiclayer deposition (ALD) or other like deposition processes. In oneembodiment, the gate conductor material that provides the gate conductorportion 74 has a thickness from 1 nm to 100 nm. Other thicknesses thatare lesser than or greater than the aforementioned thickness range canalso be employed for the gate conductor material that provides the gateconductor portion 74.

In some embodiments, and as shown, a gate cap portion 76 is present onthe gate conductor portion 74. The gate cap portion 76 may be composedof any dielectric hard mask material such as, for example, silicondioxide, silicon nitride, and/or silicon oxynitride. The dielectric hardmask material that provides the gate cap portion 76 may be formed by adeposition process such as, for example, CVD and PECVD. In oneembodiment, the dielectric hard mask material that provides the gate capportion 76 has a thickness from 1 nm to 100 nm. Other thicknesses thatare lesser than or greater than the aforementioned thickness range canalso be employed for the dielectric hard mask material that provides thegate cap portion 76.

Gate structure 70 is formed by first forming a gate material stack of,from bottom to top, the gate dielectric material, the gate conductormaterial and, if present, the hard mask dielectric material. The gatematerial stack is then patterned by lithography and etching whichprovides the gate structure 70. Lithography can include forming aphotoresist (not shown) on the topmost surface of the material stack,exposing the photoresist to a desired pattern of radiation, and thendeveloping the exposed photoresist with a resist developer to provide apatterned photoresist atop the gate material stack. At least one etch isthen employed which transfers the pattern from the patterned photoresistinto the various materials of the gate material stack. In oneembodiment, the etch used for pattern transfer may include a dry etchprocess such as, for example, reactive ion etching, plasma etching, ionbeam etching or laser ablation. In another embodiment, the etch used forpattern transfer may include a wet chemical etchant such as, forexample, KOH (potassium hydroxide). In yet another embodiment, acombination of a dry etch and a wet chemical etch may be used totransfer the pattern. After transferring the pattern into the gatematerial stack, the patterned photoresist can be removed utilizing aresist stripping process such as, for example, ashing.

As is shown in the embodiment illustrated in FIG. 20, the sidewall edgesof the gate dielectric portion 72, the gate conductor portion, and thedielectric cap portion 76 are vertically coincident to (i.e., verticallyaligned with) each other.

In some embodiments of the present application (not shown), and asmentioned above, gate structure 70 can be a sacrificial gate structure.In such an embodiment, the sacrificial gate structure may include, frombottom to top, a sacrificial gate dielectric, a sacrificial gatematerial, and a sacrificial gate cap. The sacrificial gate dielectricand/or the sacrificial gate cap are optional. When present, thesacrificial gate dielectric may include one of the dielectric materialsmentioned above for providing the gate dielectric portion 72. Whenpresent, the sacrificial gate cap may include one of the dielectric hardmask materials used in providing the gate gap portion 76. Thesacrificial gate material may be composed of polysilicon or a metal suchas Al, W, or Cu. Blanket sacrificial material layers are first formed,and then lithography and etching are used in providing a sacrificialgate structure. In such an embodiment, the sacrificial gate structure isreplaced with a permanent gate structure (as defined above) anytimeafter source/drain regions are formed.

Referring now to FIG. 21, there is illustrated the exemplarysemiconductor structure of FIG. 20 after formation of a gate dielectricspacer 78. The gate dielectric spacer 78 is formed on exposed sidewallsurfaces of the gate structure 70. A base of the gate dielectric spacer78 may be present on a topmost surface of the active silicon germaniumregion 66. The gate dielectric spacer 78 can be formed by firstproviding a spacer material and then etching the spacer material. Thespacer material may be composed of any dielectric spacer materialincluding, for example, a dielectric oxide, dielectric nitride, and/ordielectric oxynitride. In one example, the spacer material used inproviding the gate dielectric spacer 78 may be composed of silicondioxide or silicon nitride. The spacer material can be provided by adeposition process including, for example, chemical vapor deposition(CVD), plasma enhanced chemical vapor deposition (PECVD), or physicalvapor deposition (PVD). The etching of the spacer material may comprisea dry etch process such as, for example, a reactive ion etch.

Referring now to FIG. 22, there is illustrated the exemplarysemiconductor structure of FIG. 21 after forming an amorphous Si layer80. Amorphous Si layer 80 is present on exposed surfaces of the activesilicon germanium region 66 and surrounds the gate dielectric spacer 78and the gate structure 70. The amorphous Si layer 80 can be formedutilizing one of the deposition processing mentioned above for formingamorphous Si layer 18. Amorphous Si layer 80 may or may not behydrogenated. The amorphous Si layer 80 can have a thickness with therange mentioned above for amorphous Si layer 18.

Referring now to FIG. 23, there is illustrated the exemplarysemiconductor structure of FIG. 22 after forming embedded SiGesource/drain regions 82S, 82D in the active SiGe region 66 and at afootprint of the gate structure 70 utilizing a thermal mixing process inaccordance with an embodiment of the present application. During thermalmixing, Si atoms from the amorphous Si layer 80 diffuse into the activesilicon germanium region 66 and mix with the Si and Ge atoms within theactive silicon germanium region 66 to provide the embedded SiGesource/drain regions 82S, 82D. The embedded SiGe source/drain regions82S, 82D that are formed by this process have a lower germanium contentthan the remaining portion of the active silicon germanium region 66,especially the channel region that is located directly beneath the gatestructure 70. Such a structure will yield smaller lattice parametersource/drain regions and will thus create tensile strain in the channel.In cases in which the active silicon germanium region contains agermanium content of greater than 85 atomic percent, this process canresult in the ability to fabricate high mobility MOSFETs.

In accordance with the present application, thermal mixing is performedin this embodiment of the present application by annealing utilizing theconditions and ambient mentioned above in providing the structure shownin FIG. 3 of the present application. The amorphous Si layer 80 can becompletely consumed by this process. In some embodiments, a portion ofthe amorphous Si layer 80 may remain and be removed during asubsequently performed material removal process.

Although not shown, it is possible to form a dielectric material atopthe amorphous Si layer 80 prior to performing the thermal mixingprocess. The dielectric material can be removed after the thermal mixingis performed as also described hereinabove.

Referring now to FIG. 24, there is illustrated an exemplarysemiconductor structure including, an amorphous Si layer portion 80P onan active SiGe region 66 of a SGOI substrate 60 in accordance with anembodiment of the present application. In some embodiments, theamorphous Si layer portion 80P spans across the entire length of theactive SiGe region 66. In addition to the active SiGe region 66, theSGOI substrate 60 also includes a handle substrate 62 and an insulatorlayer 64. Handle substrate 62 includes one of the materials mentionedabove for handle substrate 12. Insulator layer 64 includes one of theinsulator materials mentioned above for insulator layer 14. In thepresent embodiments, active SiGe region 66 includes a patterned silicongermanium layer. In some embodiments, the active SiGe region 66 maycomprise a non-patterned silicon germanium layer. Although a singleactive SiGe region 66 is described and illustrated, a plurality ofactive SiGe regions can be present atop the insulator layer 64.

The silicon germanium layer that provides the active silicon germaniumregion 66 can be formed utilizing any of the various embodiments of thepresent application including the one described in FIGS. 18 and 19 ofthe present application. Element 68 represents dielectric structures. Insome embodiments, the dielectric structures 68 are formed prior toformation of the silicon germanium layer that provides the activesilicon region 66 (as shown, for example, in FIGS. 18 and 19 above). Inother embodiments, the silicon germanium layer that provides the activesilicon germanium region 66 is formed first, and then the dielectricstructures are formed by forming a trench (by lithography and etching)and filling the trench with a trench dielectric material.

In some embodiments (not shown), the active silicon germanium region 66can be processed into a fin structure or a nanowire structure utilizingprocesses techniques well known to those skilled in the art. When a finstructure or nanowire structure is formed, the subsequently formed gatestructure would straddle the fin structure or the nanowire structure.

The amorphous Si portion 80P can be formed utilizing one of thedeposition processing mentioned above for forming amorphous Si layer 18.Amorphous Si portion 80P may or may not be hydrogenated. The amorphousSi portion 80P can have a thickness with the range mentioned above foramorphous Si layer 18.

Referring now to FIG. 25, there is illustrated the exemplarysemiconductor structure of FIG. 24 after formation of a gate structure70 on the amorphous Si layer portion 80P and formation of a gatedielectric spacer 78. In one embodiment, the gate structure 70 may be afunctional gate structure, as defined above, and thus includes frombottom to top, gate dielectric portion 72, gate conductor portion 74 andgate cap portion 76. In another embodiment (not shown), gate structure70 is a sacrificial gate structure which is replaced with a functionalgate structure after subsequent formation of an embedded SiGe channelregion in the active SiGe region 66. The gate dielectric spacer 78 usedin this embodiment of the present applicant is the same as the gatedielectric spacer used in providing the structure shown in FIG. 21 ofthe present application.

Referring now to FIG. 26, there is illustrated the exemplarysemiconductor structure of FIG. 25 after forming embedded SiGe channelregion 86 in the active SiGe region 66 and directly beneath the gatestructure 70 utilizing a thermal mixing process in accordance with anembodiment of the present application.

In accordance with the present application, thermal mixing is performedin this embodiment of the present application by annealing utilizing theconditions and ambient mentioned above in providing the structure shownin FIG. 3 of the present application. The amorphous Si portion 80P canbe completely consumed by this process.

In accordance with this embodiment of the present application, embeddedSiGe channel region 86 has a lower germanium content that that in thesource/drain regions (to be subsequently formed and not shown herein).Such a structure will yield a smaller lattice parameter in the channelregion and will thus experience compressive strain in the channel due tothe higher germanium content surrounding the embedded SiGe channelregion 86. This structure will result in a high mobility MOSFET.

While the present application has been particularly shown and describedwith respect to various embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present application. It is therefore intended that the presentapplication not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed as new is:
 1. A method of forming a semiconductorstructure, said method comprising: forming a gate structure on an activesilicon germanium region of a silicon germanium-on-insulator material;forming an amorphous Si layer on exposed surfaces of said active silicongermanium region and surrounding said gate structure; and formingembedded SiGe source/drain regions in said active SiGe region and at afootprint of said gate structure utilizing a thermal mixing process inwhich silicon atoms from said amorphous silicon layer intermix withgermanium atoms in said SiGe active region to form said embedded SiGesource/drain regions.
 2. The method of claim 1, wherein said silicongermanium-on-insulator material is formed by a process comprising:providing a structure comprising, from bottom to top, agermanium-on-insulator substrate and an amorphous silicon layer; andconverting said structure into a silicon germanium-on-insulator materialby annealing, wherein during said annealing silicon atoms from saidamorphous silicon layer intermix with germanium atoms in a germaniumlayer of said germanium-on-insulator substrate to form a silicongermanium layer.
 3. The method of claim 1, wherein said silicongermanium-on-insulator material is formed by a process comprising:providing a structure comprising, from bottom to top, asilicon-on-insulator substrate and a germanium layer; and convertingsaid structure into a silicon germanium-on-insulator material byannealing, wherein during said annealing silicon atoms from a siliconlayer of the silicon-on-insulator substrate intermix with germaniumatoms in said germanium layer to form a silicon germanium layer.
 4. Themethod of claim 1, further comprising forming a gate dielectric spaceron sidewalls of said gate structure prior to forming said amorphoussilicon layer.